Databases Reference
In-Depth Information
Common Ground: Constructing the Bridge
Once the above design has been completed, the actual bridge can be
constructed. The bridge consists of five parts: transactions, transaction
carriers, gateways, middleware, and trigger events.
At this stage of design, the data required and the associated
update paths should be fully known and documented. Because multiple
transaction systems are not unusual, the content of the transactions must be
designed so that coherent sets of information are available during update.
Transactions.
This is the protocol of the transactions. There are
multiple levels of the communications protocol. The low level is usually
handled by the software employed (multiple communications protocols
could be involved, however, and ways of translating one protocol to anoth-
er may be required). On another level, the transaction must have ways of
identifying itself to the update software. This requires transaction identifi-
cation within the transaction itself. Routing information may also be re-
quired for complex environments.
Transaction Carriers.
The software that actually updates the database is typically
known as a gateway. In some database systems, the gateway comes as an
internal part of the database itself; with others, it must be added.
Gateways.
In extreme cases, it will be necessary to create the gateway. This kind of
gateway is likely to be the most difficult to test and debug, since all combi-
nations of data must be tested — a substantial task even for a moderate set
of transactions.
Early in the project, evaluations of existing commercial
middleware should be undertaken. There are several products on the mar-
ket with a range of capabilities, some better than others. This software can
substantially reduce the technical development and support aspect of the
project and provide significantly better control than could (or would) be
produced in-house.
Middleware.
Middleware is a generic name that refers to software that accepts and
sends transactions between disparate clients and servers, usually convert-
ing communications protocols along the way. Better commercial versions
also offer transaction reformatting and splitting.
Middleware is very effective in larger client/server systems, but requires
an initial commitment to infrastructure creation. Middleware capabilities
range from basic queuing support to full distributed computing manage-
ment environments.
The control and statistical aspects of the software are also important
because these features give the user the ability to shut down portions of
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